XENPAK is short for 10 Gigabit Ethernet Transceiver Package. When the Ethernet Network involved into a 10G network, XENPAK was invented to support the fiber optical telecommunication of such speed. It has been put into use since 2001 and belongs to one of the earlist 10G transceivers, nowadays it can only be used for some old equipments. The shape of XENPAK is pretty ponderous which can not fit the present standard, and it costs more power than the later transceivers of same functions. We can say that this kind of transceiver is nearly out of date, but we can not deny that it is a milestone during the advance of fiber optic transceivers.